WRITEV
Section: POSIX Programmer's Manual (3P)
Updated: 2013
Index
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PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
writev
--- write a vector
SYNOPSIS
#include <sys/uio.h>
ssize_t writev(int fildes, const struct iovec *iov, int iovcnt);
DESCRIPTION
The
writev()
function shall be equivalent to
write(),
except as described below. The
writev()
function shall gather output data from the
iovcnt
buffers specified by the members of the
iov
array:
iov[0],
iov[1],
...,
iov[
iovcnt-1].
The
iovcnt
argument is valid if greater than 0 and less than or equal to
{IOV_MAX},
as defined in
<limits.h>.
Each
iovec
entry specifies the base address and length of an area in memory from
which data should be written. The
writev()
function shall always write a complete area before proceeding to the
next.
If
fildes
refers to a regular file and all of the
iov_len
members in the array pointed to by
iov
are 0,
writev()
shall return 0 and have no other effect. For other file types, the
behavior is unspecified.
If the sum of the
iov_len
values is greater than
{SSIZE_MAX},
the operation shall fail and no data shall be transferred.
RETURN VALUE
Upon successful completion,
writev()
shall return the number of bytes actually written. Otherwise, it shall
return a value of -1, the file-pointer shall remain unchanged, and
errno
shall be set to indicate an error.
ERRORS
Refer to
write().
In addition, the
writev()
function shall fail if:
- EINVAL
-
The sum of the
iov_len
values in the
iov
array would overflow an
ssize_t.
The
writev()
function may fail and set
errno
to:
- EINVAL
-
The
iovcnt
argument was less than or equal to 0, or greater than
{IOV_MAX}.
The following sections are informative.
EXAMPLES
Writing Data from an Array
The following example writes data from the buffers specified by members
of the
iov
array to the file associated with the file descriptor
fd.
-
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
...
ssize_t bytes_written;
int fd;
char *buf0 = "short string\n";
char *buf1 = "This is a longer string\n";
char *buf2 = "This is the longest string in this example\n";
int iovcnt;
struct iovec iov[3];
iov[0].iov_base = buf0;
iov[0].iov_len = strlen(buf0);
iov[1].iov_base = buf1;
iov[1].iov_len = strlen(buf1);
iov[2].iov_base = buf2;
iov[2].iov_len = strlen(buf2);
...
iovcnt = sizeof(iov) / sizeof(struct iovec);
bytes_written = writev(fd, iov, iovcnt);
...
APPLICATION USAGE
None.
RATIONALE
Refer to
write().
FUTURE DIRECTIONS
None.
SEE ALSO
readv(),
write()
The Base Definitions volume of POSIX.1-2008,
<limits.h>,
<sys_uio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- Writing Data from an Array
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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